The disclosure relates generally to methods of manufacturing particulate filters and more particularly to methods of plugging and/or skinning particulate filters.
Particulate filters, such as diesel particulate filters (DPFs), are increasingly employed in pollution control systems, such as in mobile emissions applications where they are key components in most engine power train systems. Commonly used filter materials include cordierite, silicon carbide and aluminum titanate.
Particulate filters are generally made of cellular honeycomb bodies with a checkerboard plugging pattern on each side. To allow flow through the filter, the plug pattern is offset by one cell for the inlet and outlet faces. In use, particulate filters collect particulate matter, causing an increase in pressure drop across the filter. This increase in pressure drop has a negative impact on fuel economy and engine performance.
Removal of accumulated particulate matter can be accomplished via regeneration, during which engine exhaust temperatures are increased to a level in which oxidizers that are present, such as O2 and NO2 enable rapid oxidation of the soot. However, during regeneration, unfavorable conditions can sometimes exist, leading to an increase in the filter temperature and increased thermo-mechanical stresses. In extreme cases, the temperatures can cause melting and the stresses can cause fracturing of the filter. In the most extreme conditions, temperatures are especially severe in the vicinity of the outlet face of the filter and so special attention must be paid to the plug/matrix interface at the outlet side. An important characteristic of a particulate filter is, therefore, robustness under these extreme conditions.
Production of sufficiently robust plug/matrix interfaces has conventionally involved firing green plugs to a previously fired matrix material thereby involving a second firing of the matrix material. However, such production involves added processing steps and expense. On the other hand, green plugging of green matrix material has generally involved drawbacks such as insufficient airflow through the part during firing due to the fact that, when green plugs are present on both ends of a green matrix material, the composite structure is insufficiently porous, especially during the initial stage of the firing process, when no significant porosity has been created. In addition, issues of the compatibility of the green plug cement with the green body have been observed.